radiographics, V rok Lekarski CM UMK, 01 - Radiologia, materiały, radiologia - prezentacje - dane i nakradzione, 2
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//-->EDUCATION EXHIBIT285Necrotizing Enteroco-litis: Review of State-of-the-Art Imaging Find-ings with Pathologic1CorrelationCME FEATURESee accompanyingwww.rsna.org/education/rg_cme.htmlMonica Epelman, MD2●Alan Daneman, MD●Oscar M. Navarro, MDIris Morag, MD●Aideen M. Moore, MD●Jae Hong Kim, MD●RicardoFaingold, MD3●Glenn Taylor, MD●J. Ted Gerstle, MDPlain abdominal radiography is the current standard imaging modalityfor evaluation of necrotizing enterocolitis (NEC). Sonography is stillnot routinely used for diagnosis and follow-up, as it is not widely recog-nized that it can provide information that is not provided by plain ab-dominal radiography and that may affect the management of NEC.Like plain abdominal radiography, sonography can depict intramuralgas, portal venous gas, and free intraperitoneal gas. However, the ma-jor advantages of abdominal sonography over plain abdominal radiog-raphy are that it can depict intraabdominal fluid, bowel wall thickness,and bowel wall perfusion. Sonography may depict changes consistentwith NEC when the plain abdominal radiographic findings are nonspe-cific and inconclusive. Thinning of the bowel wall and lack of perfusionat sonography are highly suggestive of nonviable bowel and may beseen before visualization of pneumoperitoneum at plain abdominalradiography. The mortality rate is higher after perforation; thus, earlierdetection of severely ischemic or necrotic bowel loops, before perfora-tion occurs, could potentially improve the morbidity and mortality inNEC. The information provided by sonography allows a more com-plete understanding of the state of the bowel in patients with NEC andmay thus make management decisions easier and potentially changeoutcome.©LEARNINGOBJECTIVESFOR TEST 1After reading thisarticle and takingthe test, the readerwill be able to:Describe thepathophysiology andclinical features ofnecrotizing enteroco-litis.Discuss the imag-ing approach to diag-nosis and follow-upof necrotizing entero-colitis.Identify the imag-ing features of necro-tizing enterocolitis.TEACHINGPOINTSSee last pageRSNA, 2007Abbreviation:NECnecrotizing enterocolitisRadioGraphics 2007;27:285–305●Published online10.1148/rg.272055098●Content Codes:1Fromthe Department of Diagnostic Imaging (M.E., A.D., O.M.N., R.F.) and Divisions of Neonatology (I.M., A.M.M., J.H.K.), Pathology (G.T.),and General Surgery (J.T.G.), Hospital for Sick Children and University of Toronto, 555 University Ave, Toronto, Ontario, Canada M5G 1X8. Re-cipient of a Certificate of Merit award and an Excellence in Design award for an education exhibit at the 2004 RSNA Annual Meeting. Received April19, 2005; revision requested June 21; final revision received August 10, 2006; accepted August 23. J.H.K. is a consultant for Abbott Nutrition, AbbottPark, Ill; all other authors have no financial relationships to disclose.Address correspondence toA.D. (e-mail:alan.daneman@utoronto.ca).address:Department of Radiology, Children’s Hospital of Philadelphia, Philadelphia, Pa.address:Department of Radiology, Montreal Children’s Hospital, Montreal, Quebec, Canada.2Current3Current©RSNA, 2007286March-April 2007RGfVolume 27●Number 2Figure 1.Pathologic findings in NEC.(a)Histologic section of small bowel (original magnification, 100; he-matoxylin-eosin stain). Intramural gas is seen as rounded bubbles in the submucosa (arrows). There is hyperemiaof the serosa.(b)Histologic section of small bowel (original magnification, 100; hematoxylin-eosin stain). Thebowel is affected much more severely than ina.There is necrosis of the mucosa, submucosa, and muscularis withintraluminal necrotic debris on the mucosal side of the bowel wall(m).Only the serosa appears intact.sserosalsurface of bowel wall.(c)Postmortem photograph of bowel involved with severe NEC. The arrows indicate areasof the bowel wall where there has been so much necrosis and sloughing of the mucosa, submucosa, and muscularisthat only the serosa is intact. One can see through these areas of the serosa into the lumen of the bowel.IntroductionNecrotizing enterocolitis (NEC) is a commonacute abdominal condition seen in the neonatalperiod. Early diagnosis, which relies on imagingfindings, and institution of prompt therapy areessential to limit morbidity and mortality.The purpose of this article is to review currentconcepts of the role of imaging in neonates withNEC. We would like to reaffirm the importanceof plain abdominal radiography as the currentstandard imaging modality in this entity and toalso emphasize the important role that sonogra-phy may play. Sonography is still not routinelyused, as it is not widely recognized that it can pro-vide information that is not depicted on radio-graphs and that may indeed affect management ofpatients with NEC.This article discusses the pathophysiology,clinical findings, and imaging features depictedwith plain abdominal radiography and abdominalsonography in NEC.PathophysiologyThe etiology and pathogenesis of NEC remaincontroversial. It is believed that NEC is secondaryto a complex interaction of multiple factors, nota-bly prematurity, that result in mucosal damage,which leads to intestinal ischemia and necrosis(1,2). The mucosal injury may be due to infec-tion, intraluminal contents, immature immunity,release of vasoconstrictors, and inflammatory me-diators (3,4). The loss of mucosal integrity allowspassage of bacteria and their toxins into the bowelwall and then into the systemic circulation, result-ing in a generalized inflammatory response andoverwhelming sepsis in the severe forms of NEC(4).The inflammatory process in NEC leads toincreased blood flow in the affected bowel seg-ment. Bacteria penetrate the mucosal defense,and their by-products of metabolism lead to theformation of intramural gas (Fig 1). As NECprogresses, platelet-activating factor produced byinflammatory cells and bacteria propagate theinflammatory cascade, mainly that of cytokinesRGfVolume 27●Number 2Epelman et al287and complement, leading to extensive transmuralinvolvement (5,6). Eventually, there is compro-mise of the microvasculature such that ischemicchanges to the tissue occur. Finally, the nonper-fused bowel wall undergoes necrosis, which maybe so severe that sloughing of the bowel wall oc-curs, resulting in bowel wall thinning and eventu-ally perforation (Fig 1).Clinical FindingsNEC is one of the most common acquired, life-threatening gastrointestinal diseases in the new-born, affecting 1%–5% of neonatal intensive careunit admissions and up to 10% of neonates under1500 g (7). The incidence of NEC is inverselyproportional to the gestational age (8,9). Infantsof 28 weeks or less gestational age and those ofextremely low birth weight (less than 1000 g) areat a greater risk for NEC (10). However, approxi-mately 10% of neonates with NEC are born atterm, and congenital heart disease is the main riskfactor in this group (7,9,11,12). Other risk factorsinclude perinatal asphyxia, patent ductus arterio-sus, indomethacin therapy, and decreased umbili-cal flow in utero (12–14).NEC most commonly manifests within thefirst or second week of life. However, the time ofpresentation varies with the gestational age; invery premature neonates, NEC may manifestonly in the second or third week of life (6,9,15).The clinical diagnosis of NEC is often a chal-lenge, as the presentation may vary considerably,is frequently nonspecific, and may be indistin-guishable from neonatal sepsis. The symptomsreferable to the gastrointestinal tract include feed-ing intolerance, vomiting, diarrhea, and blood inthe stool (15). However, there may also be non-specific generalized symptoms including lethargy,temperature and blood pressure instability, andapnea. Physical signs include abdominal disten-tion and, in more advanced cases, palpable, dis-tended bowel loops and abdominal wall erythemaand edema. Neonates with severe disease mayeven present in shock (15).Prompt institution of therapy, which includesbowel rest with a nasogastric tube, antibiotics,and adequate hydration (total parenteral nutri-tion), is essential to limit clinical progression andthe development of complications. Clinical dete-rioration may result from generalized sepsis orbowel necrosis, which may progress to perforationand the development of peritonitis or intraab-dominal abscesses. Bowel perforation occursin 12%–31% of patients (16). A continuingchallenge to the surgeon and radiologist alike isthe determination when the most appropriatetime for surgical intervention is in those neonateswho are not responding to medical therapy orhave developed complications. Pneumoperito-neum is the only radiologic sign that has beenuniversally agreed on as an indication for surgicalintervention, and this is complicated by the factthat not all neonates with bowel necrosis and per-foration have free gas at plain abdominal radiog-raphy (15,17).The overall mortality rate in NEC is between20% and 40% and is higher in neonates of verylow birth weight (15). Mortality climbs to 64%for the very low birth weight infant once perfora-tion has occurred (18,19). Because of the highermortality rate following perforation, earlier detec-tion of severely ischemic or necrotic loops ofbowel before perforation occurs could potentiallyimprove the morbidity and mortality in NEC(17). Imaging may therefore play an importantrole in this regard (17).Imaging ModalitiesThe imaging modalities that are used in neonatesduring the active phase of NEC include plain ab-dominal radiography and abdominal sonography.Studies that have evaluated the use of contrastexaminations of the gastrointestinal tract, com-puted tomography, and magnetic resonance im-aging will not be addressed, as these modalitieshave not been found to be useful in clinical prac-tice (15,20 –23).Plain Abdominal RadiographyPlain abdominal radiography is the current mo-dality of choice for the evaluation of neonates sus-pected of having NEC.The timing of follow-upplain abdominal radiographs depends on the se-verity of the NEC and may vary from 6 to 24hourly. However, plain abdominal radiographsare also required at any time of acute clinical de-terioration. In those patients who are resolvingclinically, the time interval between plain abdomi-nal radiographs can be progressively prolonged(24).At the time of diagnosis, plain abdominal radi-ography must include one image obtained witha vertical beam with the patient supine and asecond image obtained with a horizontal beamTeachingPoint288 March-April 2007RGfVolume 27●Number 2(Fig 2). We prefer to obtain a cross-table viewwith the patient still supine, as this has the advan-tage that one does not have to move these sickand often labile patients. Both vertical and hori-zontal beam views are required for follow-up inthe first 48 hours following diagnosis, as the vastmajority of perforations occur in this time frame(24). After this, vertical beam views alone maysuffice unless there is specific concern for perfora-tion.The main observations to be made on the plainabdominal radiograph relate primarily to the pres-ence, amount, and distribution of gas, which in-cludes intraluminal gas, intramural gas, portalvenous gas, and free intraperitoneal gas (Fig 2).From observations of the intraluminal gas, it maysometimes be possible to make inferences regard-ing the presence of bowel wall thickening, freefluid, and focal fluid collections.Abdominal SonographyThe major advantages of abdominal sonography(US) in NEC are that it provides, in real time,direct images of abdominal structures, particu-larly the bowel, and of fluid in the peritoneal cav-ity.Initial studies to evaluate the role of abdominalUS in NEC date back to 1984, but no systematicstudies—to our knowledge— compared the find-ings of abdominal US with those of plain abdomi-nal radiography and how these findings may affectmanagement (16,19,25–36). The emerging roleof abdominal US has become particularly evidentwith the recent publication in 2005 of the firststudy that assessed bowel viability with colorDoppler sonography in neonates with NEC (17).In that study, Faingold et al (17) established datafor bowel wall thickness, echogenicity, peristalsis,and perfusion in the normal neonate and in thosewith NEC (Fig 3). Their findings showed thatabdominal US including color Doppler sonogra-phy was extremely helpful for facilitating patientmanagement. Further corroboration of the utilityof abdominal US in NEC can also be found intwo recent articles by Kim et al (37,38), who con-cluded that evaluation of the bowel wall withgray-scale US was helpful for diagnosis of NEC.It is important to emphasize here that meticuloustechnique with use of state-of-the-art equipmentis essential, and in this regard high-megahertzlinear-array transducers are invaluable for depict-ing the bowel optimally.Figure 2.Supine(a)and cross-table lateral(b)ra-diographs of the abdomen obtained in a neonate withNEC. The bowel is mildly dilated with gas, mainly onthe left side. The bubbly pattern of gas seen mainly inthe right lower quadrant represents intramural gas.Free intraperitoneal gas is present anteriorly (arrowsinb).Unfortunately, there are no large publishedstudies—to our knowledge— comparing the abil-ity of plain abdominal radiography and abdomi-nal US to depict the abnormalities in neonateswith NEC. Abdominal US can certainly depictthe gas patterns in the abdomen described in thesection on plain abdominal radiography. Al-though there are limited data available, on thebasis of our recent experience we believe that ifmeticulous attention is paid to technique, ab-dominal US is in fact more sensitive in detectingintramural gas and portal venous gas and possiblyeven free gas than plain abdominal radiography(17). This correlates with what has been shownexperimentally and clinically in the two studies byKim et al (37,38). However, what is even moreimportant is that abdominal US offers severalRGfVolume 27●Number 2Epelman et al289Figure 3.Sonographic appearances of normal bowel in a neonate.(a)Gray-scale imageshows the typical appearance of collapsed bowel. The echogenic linear markings representthe mucosal interface with the lumen, and the surrounding hypoechoic bands represent themuscularis of the bowel wall.(b)Color Doppler image of normal collapsed bowel showscolor dots of flow in the arteries of the bowel wall.Figure 4.Supine radiograph of the abdomen of anormal neonate shows a normal bowel gas pattern. Gasis distributed throughout the small and large bowel,and it is difficult to differentiate the small bowel fromthe large bowel. Each loop causes impressions on adja-cent loops, giving each loop a multifaceted appearance;the overall pattern resembles that of a mosaic. Theloops are generally not rounded or elongated.power Doppler imaging to show the presence orabsence of bowel wall perfusion (17).Abdominal US does have some relative limita-tions. Large amounts of bowel gas may makesonographic evaluation of the abdomen difficult,although we have found this to be a problemin only small numbers of neonates with NEC.Faingold et al (17) found that the gray-scale andcolor Doppler sonograms were not interpretablebecause of large amounts of bowel gas in only twoof 32 neonates with NEC or at risk for NEC. Theother limitations relate to the patient’s condition.Abdominal US should not be attempted in anyneonate who is labile or unstable, and we haverefrained from performing abdominal US if ab-dominal tenderness is such that holding the trans-ducer on the abdomen causes the patient severediscomfort. However, using a large amount of gelon the abdominal wall may facilitate performanceof the study by enabling images to be obtainedwithout the transducer actually touching the ab-dominal wall.Imaging FindingsBowel Gas PatternIn normal neonates, gas is most often presentthrough most of the small and large bowel andeach gas-filled loop causes an impression on adja-cent loops. The loops develop a multifaceted con-figuration, giving the gas pattern a “mosaic” ap-pearance (Fig 4). The small and large bowel mayother clear advantages over plain abdominal radi-ography, as it has the ability to depict bowel wallthickness and echogenicity as well as free and fo-cal fluid collections and their character much bet-ter than plain abdominal radiography (16,39).Furthermore, real-time abdominal US can depictsome features that plain abdominal radiographycannot depict at all. These include the ability todepict peristalsis and the ability of color and
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